SUMMARY PROJECT 2: Majority of cancer patients will die of metastases originating from disseminated tumor cells (DTCs), years or even decades after treatment. This suggests that DTCs survive in a dormant, non-proliferative state. However, because the biology of DTCs is poorly understood it is critical to ask basic mechanistic questions to further develop translational approaches. Our goal is to identify these mechanisms by combining powerful In vivo models and novel imaging and nano-device technologies available through this collaboration. This consortium provides unprecedented synergy to study dormancy and address three emphasis areas of this RFA: 1) tumor dormancy, activation of dormant cells and the tumor microenvironment (SAI), and dormancy in response to cancer treatment (SA2); 2) imaging the tumor microenvironment during tumor metastasis, and dormancy (SAI), as well as in response to therapies (SA2) and 3) characterization and functional relevance of the tumor microenvironment extracellular matrix (ECM) and how tumor cells stroma interactions (i.e. niches) establish metastatic cell fate (SA2). We hypothesize that at least two scenarios influence DTC dormancy. Scenario 1: DTCs from invasive cancers activate stress signals in response to a growth-restrictive target organ microenvironment inducing dormancy. Scenario 2: therapy and/or micro-environmental stress conditions (e.g. hypoxia) acting on primary tumor cells carrying a dormancy signature primes newly DTCs to enter dormancy. Based on these two scenarios we propose to 1) isolate DTCs and identify microenvironment-specific gene programs driving DTC dormancy (Scenario 1) and 2) determine whether primary tumor stress microenvironments trigger long-term dormancy of DTCs (Scenario 2). Findings in both aims will be validated using archived human primary and metastatic tumors. using human squamous (HEp3) and mouse breast carcinoma models (MMTV-Neu), we found that low ERK1/2 (mitogenic) and high p38a/p (stress) signaling activated dormancy of DTCs. Tumor cells spontaneously disseminated to lungs, lymph nodes (LN) and bone marrow (BM). A short-term dormancy period (2-3 weeks) preceded expansion of lung DTCs. However, BM DTCs persisted in a dormant state (Scenario 1). Systemic inhibition of p38a/p eliminated the short-term dormancy of lungs DTCs and also fueled growth even in sites where it is never observed like spleen, liver and BM. Thus, DTCs might remain occult and dormant in growth restrictive sites (Scenario 1). We also identified a specific gene expression program (signature) in dormant HEp3 cells that is present in cell lines derived from BM DTCs. Importantly, patients whose breast primary tumors carried this dormancy gene signature remained metastasis free for longer periods than those negative for the signature (Scenario 2). We also found that exposure to sub-lethal doses of y-radiation or oxidative stress ignited in surviving cells a dormancy state (Scenario 2). These preliminary data further support the important progress we have made in understanding the scenarios we propose to explore in our specific aims.